Extent Structure
An extent is a collection of contiguous pages within a dbspace. Every permanent database table has two extent sizes associated with it. The initial-extent size is the number of kilobytes allocated to the table when it is first created. The next-extent size is the number of kilobytes allocated to the table when the initial extent, and every extent thereafter, becomes full.
Blobspaces do not use extents.
For specific instructions on how to specify and calculate the size of an extent, see your IBM® Informix® Performance Guide.